Instant speed sacking would make this broken, but it's not bad at all the way it is. This allows you to tutor up beasts from your deck, and to have the right enter and leave battlefield effects when you need them. And you can always swing with your creature before sacrificing it, doing away with those weakened by -1/-1 counters. It's an utility card, that allows you to play less copies of what you need. And of course it's not broken like Aether Vial, but it still gives you some uncounterable creatures, pushes you up the curve even without the mana for it, even more if you play something with Phyrexian mana... In general it's a solid card, I got to play with it on the pre-release, fetching the Obliterator...

I really wanna play this card.. I don't think its overpowered or anything but damn would it be reeeeally fun to use. Toolbox decks where you can many options are my favorite kind, and this would just be sooo fun to play. Probably very very easy to disrupt though. Maybe Black Green for some reanimator action? I was skeptical, but I dig.

I want to abuse this as much as possible by making a Birthing Pod Soulshift deck.That way every time I sacrifice a creature, I'll get one bigger one from my library and one smaller one from my graveyard.

1 drops should probably mainly be mana ramp, birds, llanowar elves, treespeaker (works well with myr superion) to get a turn 2 pod
2 drops, probably have myr superion's as a 4 of, can be played with the pod or off of treespeakers.
a very good 3 cmc card for this is trinket mage as it allows you to restart the system with a hex parasiteor similar (then potentially getting another myr superion)
4 drop entomber exarch for some nice disruption
5 drop acidic slime, more nice desruption.
6 drop frost titan seems nice if you like the disruption.

a pretty good 5 drop alternative is clone shell, as it can by itself get you big creatures, or just be a bridge from 4 to 6 that gives you an extra creature (card advantage and a restart if they kill your big creature).

Could be devastating if played in conjunction with Remembrance, effectively replacing the sacrificed creature with a copy. Even better if you also use a way to get the original card out of the graveyard, like Guiding Spirit or Volrath's Stronghold.